1) Field of the Invention
The invention relates to a process for the preparation of bitumen/polymer compositions with improved mechanical properties. It further relates to the application of the compositions obtained to the production of pavements, and in particular of road surfacings, of bituminous mixes or else of watertight facings, and it also relates to a mother solution of polymers which can be employed for obtaining the said compositions.
2) Background Art
It is known to employ bituminous compositions as various surface coatings and especially as road surfacings, on condition that these compositions have a certain number of essential mechanical properties.
These mechanical properties are in practice assessed by determining, using standardized tests, a series of mechanical characteristics, the most widely employed of which are the following:
softening point, expressed in .degree. C. and determined by the ring-and-ball test defined by NF Standard T 66 008, PA1 brittleness point, or Fraass point, expressed in .degree. C. determined according to IP Standard 80/53, PA1 penetrability, expressed in 1/10 of a mm and determined according to NF Standard T 66 004, PA1 tensile rheological characteristics, determined according to NF Standard T 46 002, and comprising the quantities: PA1 (a) random copolymers of ethylene and of vinyl acetate and random copolymers of ethylene and of alkyl acrylate or methacrylate containing a C.sub.1 -C.sub.6 alkyl residue, such as methyl, ethyl, propyl, butyl or hexyl, which contain, by weight, 40% to 99.7%, and preferably 50% to 99%, of ethylene; PA1 (b) random copolymers of ethylene and of a monomer B chosen from acrylic acid, methacrylic acid, maleic acid or its anhydride, glycidyl acrylate and glycidyl methacrylate, which contain, by weight, 80% to 99.7%, and preferably 85% to 99.5%, of ethylene; PA1 (c) random terpolymers of ethylene, of a monomer A chosen from vinyl acetate and alkyl acrylates or methacrylates containing a C.sub.1 -C.sub.6 alkyl residue such as methyl, ethyl, propyl, butyl or hexyl, and of a monomer B chosen from acrylic acid, methacrylic acid, maleic acid or its anhydride, glycidyl acrylate and glycidyl methacrylate, which contain, by weight, 0.5% to 40% of units derived from the monomer A and 0.5% to 15% of units derived from the monomer B, the remainder being formed by units derived from ethylene; and PA1 (d) the copolymers resulting from the grafting of a monomer B chosen from acrylic acid, methacrylic acid, maleic acid or its anhydride, glycidyl acrylate and glycidyl methacrylate, onto a substrate consisting of a polymer chosen from polyethylenes, especially low density polyethylenes, polypropylenes and the random copolymers defined under (a), the said graft copolymers containing, by weight, 0.5% to 15% of grafted units originating from the monomer B. PA1 (i) random terpolymers of ethylene, of alkyl acrylate or methacrylate containing a C.sub.1 -C.sub.6 alkyl residue such as methyl, ethyl or butyl, and of maleic anhydride, which contain, by weight, 0.5% to 40% of units derived from alkyl acrylate or methacrylate and 0.5% to 15% of units derived from maleic anhydride, the remainder being formed by units derived from ethylene; PA1 (ii) random terpolymers of ethylene, of alkyl acrylate or methacrylate containing a C.sub.1 -C.sub.6 alkyl residue such as methyl, ethyl or butyl, and of glycidyl acrylate or methacrylate, which contain, by weight, 0.5% to 40% of units derived from alkyl acrylate or methacrylate and 0.5% to 15% of units derived from glycidyl acrylate or methacrylate, the remainder being formed by units derived from ethylene; PA1 (iii) maleic anhydride-grafted low density polyethylenes and maleic anhydride-grafted poly-propylenes, which contain, by weight, 0.5% to 15% of grafted units derived from maleic anhydride.
yield stress .sigma.y, in bars, PA2 yield elongation .epsilon.y, in %, PA2 breaking stress .sigma.b, in bars, PA2 elongation at break .epsilon.b, in %.
An indication of the temperature susceptibility of the bituminous compositions can also be obtained from a correlation between the p en etrability (abbreviated to pen) and the softening point (abbreviated to RBT) of the said compositions, known by the name of Pfeiffer's number (abbreviated to PN).
This number is calculated using the relation: EQU PN=(20-500 A)/(1+50 A)
in which A is the slope of the straight line represented by the equation: EQU A=(log.sub.10 800-log.sub.10 pen)/(BRT-25)
The temperature susceptibility of the bituminous composition is proportionally lower the greater the value of Pfeiffer's number or, what amounts to the same thing, the lower the value of the quantity A. In the case of conventional bitumens, Pfeiffer's number assumes values which lie in the neighborhood of zero.
In general, conventional bitumens do not simultaneously exhibit the combination of the required properties and it has been known for a long time that the addition of various polymers to these conventional bitumens allows the mechanical properties of the latter to be favourably modified and bitumen-polymer compositions to be formed which have mechanical properties that are improved in relation to those of bitumens alone.
The polymers liable to be added to the bitumens are in most cases elastomers such as polyisoprene, butyl rubber, polybutene, polyisobutene, ethylene/vinyl acetate copolymers, polymethacrylate, polychloroprene, ethylene/propylene/diene (EPDM) torpolymer, polynorbornene or else random or block copolymers of styrene and of a conjugated diene.
Among the polymers which are added to bitumens, random or block copolymers of styrene and of a conjugated diene, and especially of styrene and butadiene or of styrene and isoprene, are particularly effective because they dissolve very easily in bitumens and endow them with excellent mechanical and dynamic properties and especially with very good viscoelasticity properties.
It is further known that the stability of the bitumen-polymer compositions can be improved by chemical coupling of the polymer to the bitumen, this improvement in addition making it possible to widen the field of use of the bitumen-polymer compositions.
Bitumen-polymer compositions in the case of which a random or block copolymer of styrene and of a conjugated diene, such as butadiene or isoprene, is coupled to the bitumen can be prepared by making use of the processes described in references FR-A-2376188, FR-A-2429241, FR-A-2528439 and EP-A-0360656. In these processes the said copolymer and a source of sulphur are incorporated into the bitumen, the operation being carried out between 130.degree. C. and 230.degree. C. and with stirring, and the mixture thus formed is then kept stirred and at a temperature between 130.degree. C. and 230.degree. C. for at least fifteen minutes. The source of sulphur consists of chemically unbonded sulphur (FR-A-2376188 and FR-A-2429241), of a polysulphide (FR-A-2528439) or of a sulphur-donor vulcanization accelerator employed by itself or in combination with chemically unbonded sulphur and/or a polysulphide or a vulcanization accelerator which is not a sulphur-donor (EP-A-0360656) and the incorporation of the copolymer and of the source of sulphur into the bitumen is carried out either by direct addition of the said ingredients to the bitumen (FR-A-2376188, FR-A-2528439 and EP-A-0360656) or else by first of all preparing a mother solution of the copolymer and of the source of sulphur in a hydrocarbon oil and then by adding the said mother solution to the bitumen (FR-A-2429241, FR-A-2528439 and EP-A-0360656).